Conventional elevators illustratively have a car arranged for travel along a vertical hoistway, a rope to move the car upward or downward in the hoistway, the rope firmly connected to the car at one extremity of the rope, a counterweight to compensate the weight and the payload of the car, the counterweight firmly connected to the rope at the other extremity thereof, and a traction machine such as an electric motor for driving the rope.
In this typical configuration of existing elevators, however, the present inventor believes that several disadvantages may lie, for example:
Both large and heavy equipment such as a traction machine, a drum, and a sheave are typically installed at the top or the bottom of the hoistway. This requires extra space for installation of those equipment in the building.
Wear of the rope and the sheave should be frequently monitored so as to satisfy the elevator satiety standard.
Guiding facilities for the car and the counterweight must be provided in the hoistway; thus, the whole structure of the hoistway tends to be complicated. This also results in high construction costs.
In order to overcome these perceived shortcomings of the existing elevators, several proposals have been made in the art.
One of these proposals is a self-propelled elevator employing a linear motor as a traction mechanism. In this type of an elevator system, the primary of the linear motor is installed either on the car or on the inner surface of the hoistway in the building and the secondary is attached as faced the primary with a certain gap. See, for example, U.S. Pat. No. 5,203,432 to Grinaski entitled "Flat Linear Motor Driven Elevator." However, the present inventor believes that this configuration still is less than entirely satisfactory:
The construction cost of the system may be sometimes expensive and not commercially viable without superconductivity or equivalent.
The linear motor is often undesirable, compared with conventional ac/dc motors, in terms of power consumption, because of low efficiency and low power factor. See also U.S. Pat. No. 5,158,156 to Okuma et.al. entitled "Linear Motor Elevator with Support Wings for Mounting Secondary Side Magnets on an Elevator Car."
On the other hand, Canadian laid-open patent publication No. 2,079,096, entitled "Lift, in Particular Inclined Lift" describes the following structure.
The two lift rails follow the path of a winding staircase and are fixed to the wall at a constant vertical distance apart. On the lift cage frame is an upper pivot plate with a driven roller and opposing spring-loaded roller between which the top rail is gripped. Smaller guide rollers align the pivot plate on the rail. A motor and gearbox drive onto the shaft of the driven roller. A chain transmits the driving force to an identical lower pivot plate and assembly gripping the bottom rail. Thus, the lift of this disclosure can be self-propelled along the two rails. However, this technique may still have the following drawbacks:
The driving force transmission mechanism may be complicated because of the gearbox and the chain. Frequent maintenance is sometimes necessary to keep reliable operation.
Because the driving force transmission mechanism is disposed on the car, the noise emitted from the mechanism may be high enough to make passengers feel less comfortable sometimes.